1. Field of the Invention
The present invention relates to a semiconductor storage element that uses a ferroelectric substance, and more particularly to a wiring layer structure for a ferroelectric capacitor.
2. Description of Related Art
Ferroelectric storage that uses ferroelectric material as the material for the capacitor is now reaching a stage for practical use as a type of non-volatile device. It is expected that memory devices equipped with ferroelectric capacitors will require low voltage, will have low power consumption, and will operate at high speeds because of the characteristics of this ferroelectric material. However, solutions to a number of problems are required before capacitor configurations that include ferroelectric materials can be applied in conventional semiconductor devices.
One of these problems is the degradation of the characteristics of thin ferroelectric films by hydrogen. Many of the ferroelectric materials that have been examined for application in memory are oxides of a multiplicity of elements. Typical such metal oxide materials include SrBi2Ta2O9 (abbreviated to SBT), and Pb(Zr, Ti) O3. After formation of a ferroelectric capacitor configuration using these materials, if activated hydrogen (hydrogen radical: H*) or molecular hydrogen (H2) is activated during the processes that complete a semiconductor device, these hydrogen radicals reduce the oxygen in the ferroelectric material and therefore the oxygen in the thin ferroelectric film. This reduction causes degradation of the characteristics of the ferroelectric material in the thin ferroelectric film.
One method used to combat this degradation in characteristics is recovery annealing in oxygen at a temperature at which the ferroelectric substance crystallizes, that is at a temperature between 700° C. and 800° C. Another method used is the formation of a barrier metal around the capacitor structure itself to prevent the infiltration (or entering) of activated hydrogen or molecular hydrogen into the thin ferroelectric film.
However, when semiconductor devices that include these memory devices are integrated or consolidated, a process to form wiring that is connected to the capacitor of the memory device is implemented. This wiring material is usually aluminum. Therefore, after the capacitor structure is formed, annealing at temperatures of 700° C. and above, as described above, cannot occur.
Also, for example, Document 1, Densijouhou Tuusin Gakkai Ronbunsi C Vol. J83-C No. 1 pp. 53-59 (2000), discloses an example in which aluminum (Al) wiring is formed in the capacitor structure and an inter-layer insulation film, made of an ozone TEOS film (oxide film) is formed on the upper side of this wiring.
The document points out that:    (a) The ozone TEOS film produces large quantities of moisture;    (b) The moisture produced produces hydrogen when it oxidizes the Al;    (c) This hydrogen degrades the characteristics of the thin ferroelectric layer; and    (d) This degradation can be reduced by using a TiN (titanium nitride) layer on the Al wiring substrate since the addition of this TiN causes less hydrogen to be produced than when Al alone is used. This is because TiN oxidizes more than Al.
Also, Document 2, Japanese Patent Application Laid-open No: 10-177991, discloses a semiconductor device configured so that the Al or Al radical alloy wiring layer, formed on a titanium nitride (TiN) film, which is the barrier metal, does not corrode. According to this Document 2, ion sputtering of this insulation film is carried out on the side wall of a wiring structure created by laminating layers of titanium nitride, Al or an Al radical alloy, and titanium nitride on this insulation film, which is made for example from silicon dioxide. This forms a corrosion protection film (sputter material film) that prevents infiltration (or entering) of moisture from the outside onto the Al or Al radical alloy.
However, neither Document 1 nor Document 2 disclose or suggest a wiring layer structure or formation method thereof that can be applied in a wiring layer (or interconnection layer) that comes into direct contact with the electrodes of the ferroelectric capacitor.
Accordingly, there has been a demand for some means of preventing the degradation of the characteristics of a thin ferroelectric film caused by the wiring after such contact wiring is formed.